1. Field of the Invention
This invention relates to a focal-plane shutter for digital still cameras which is designed to actuate a first blade and a second blade in turn in the same direction when photographing is performed and to expose an imaging surface through a slit provided by both blades.
2. Description of Related Art
In focal-plane shutters used in digital still cameras, some types of shutters are known in accordance with the specifications of cameras. One of them, like a focal-plane shutter used in a film camera, is equipped with a first blade and a second blade to actuate these blades in turn at predetermined timing so that an imaging surface is exposed continuously from its one side to the other through a slit provided by the blades.
Digital still cameras using shutters constructed as mentioned above are divided into two classes, those in which an optical finder is provided as in the film camera so that the imaging surface is covered by at least one of the first blade and the second blade, except for the case where photographing is performed, and those, having finders referred to as electronic view finders, in which the entire surface in an exposure aperture is exposed to light from an object so that an image of the object can be observed through a monitor, even when photographing is not performed. Thus, the latter camera is such that, in photography, the first blade is moved to the position where the imaging surface is covered, and then an exposure operation is performed.
In the film camera, the area of the imaging surface is usually larger than that of the digital still camera. The film camera always has the optical finder. Due to the arrangement of an optical system and the placement of a film, each of the first blade and the second blade is composed of a plurality of blade components to achieve compactness of a shutter unit. However, in the digital still camera, particularly provided with the electronic view finder, each of the first blade and the second blade need not necessarily be constructed with a plurality of blade components, and is also known to have a single blade component. An example of a shutter constructed from such a viewpoint is shown in FIG. 1 (refer to Japanese Patent Preliminary Publication No. Hei 11-326992).
Since the focal-plane shutter for digital still cameras mentioned above, in contrast with that for film cameras, is not subjected to severe restriction of space, each of the first blade and the second blade, as described above, can be constructed with a single blade component. However, if the entire shutter unit is enlarged, the number of degrees of design freedom of a camera will be limited in inverse proportion to shutter size, and the possibility of using this shutter unit will diminish. Thus, apart from the number of blade components of each of the first blade and the second blade to be constructed, at least, compactness of the entire shutter unit is the maximum requirement, together with cost reduction thereof.
When the conventional example shown in FIG. 1 is considered from such a standpoint, the shutter is constructed so that the vertical dimension of a base plate 101 must be essentially increased. Specifically, in FIG. 1, a second blade 105 is located at a higher position than a first blade 102, and when the exposure operation is performed, the second blade 105 passes the place of the first blade 102 and then blocks an optical path AP. Thus, the conventional example, in contrast with an ordinary shutter, unnecessarily provides a space for the second blade 105 and must increase the vertical dimension of the base plate 101 accordingly.
In the conventional example mentioned above, even though each of the first blade 102 and the second blade 105 is constructed with a plurality of blade components, it is impossible to obtain further compactness of the shutter unit. Specifically, for example, if the first blade 102 and the second blade 105 are constructed with respective two blade components and are arranged as in FIG. 1 in a state where the respective two blade components are completely superimposed, the dimension above the optical path AP will be approximately halved. In this case, however, the two blade components of the first blade, after blocking the optical path AP in a state where the amount of mutual superposition is minimized, are moved downward by the same amount as in this state, and thus the dimension below the optical path AP is required twice. As a result, the upper and lower dimensions of the base plate 101 unit cannot be reduced.
In particular, when the focal-plane shutter is used, it is necessary to actuate each of the shutter blades at a high speed in photography. Thus, it is common practice to use a spring as a driving source of the shutter blade. However, when the shutter blade is restored to a state before photography against the biasing force of the spring, it is common practice to use a motor as a driving source of the shutter blade. In most cases, the exposure aperture is opened and closed by moving the shutter blades vertically in an ordinary photographing posture in which a camera is held by hands on both sides thereof.
A conventional digital camera using such a focal-plane shutter has been initially designed to follow the appearance of the film camera. However, in recent years, the low cost and high image quality of a CCD have been achieved, and the digital camera has exceeded the film camera in sales. As such, the design of appearance of the digital camera itself has been developed and as a result, peculiar compactness or downsizing of the internal structure of the camera has become necessary. Techniques for such compactness are disclosed, for examples, in Japanese Patent Preliminary Publication Nos. Hei 11-261863 and Hei 11-218838.
Specifically, in Hei 11-261863, as shown in FIGS. 1 and 2 of this publication, the internal area of the casing of the camera is partitioned by an image display circuit substrate 19, a partition plate 20, a first record compaction circuit substrate 21, and a first imaging circuit substrate 16, and is divided into a middle space 23A, a first side space 23B, and a second side space 23C so that electrical parts are arranged efficiently with respect to the function and radiation in each space. In a grip 5, parts of a record compaction circuit system are arranged. In particular, by this construction, a rise in temperature of an image sensor 8 caused by the convection of air can be prevented and at the same time, compactness of a casing 2 can be achieved.
In this case, compactness is also required for the shutter constituting the camera, and an example of this is set forth in Hei 11-218838. According to this example, in FIGS. 1, 2, and 6 of this publication, an imaging unit 73 is placed so that its one end on the side of a photographing lens 45 projects into a second aperture 63a of a frame 63 on the imaging unit side. Since a shutter blade 67a is placed on the side of the photographing lens 45, shutter blades 67a-67e are deflected by a shock produced when a shutter screen 65 is closed, but the shutter is designed so that the shutter blades do not come in contact with the imaging unit 73. A length along the optical path of the photographing lens can thus be reduced, and it is possible to achieve compactness of the camera.
As mentioned above, the camera of Hei 11-261863 is constructed so that the arrangements of parts of electric circuits are changed and thereby the size of the casing can be diminished. Even in this case, however, space surrounded by heavy dotted lines in FIGS. 1 and 2 of the publication still leaves room for compactness. The shutter unit is to be placed in this space, but if the shutter unit of Hei 11-218838 is used, it is conceivably possible to place this shutter unit in the space. It is an unquestionable fact, as described above, that the focal-plane shutter for digital still cameras in the future is subjected to restrictions from viewpoints different from those in the past and must be designed to meet the demand of compactness or downsizing accordingly.
The focal-plane shutter, as mentioned already, uses the spring as the driving source for actuating the shutter blade in photography and the motor as the driving source for restoring it to a state before photography. In a conventional focal-plane shutter, however, the motor is mounted on the camera body side, and thus when the shutter unit is incorporated in the camera body, both must be connected through wheels. The placement of such a transmission mechanism and the construction of a connection require a relatively wide space and high cost. However, the digital still camera, like the film camera, sometimes has no stop mechanism. Even though the camera is provided with the stop mechanism, there may be no need to have the motor in common. There may be no need to have the motor in common with a mirror drive, or a mirror mechanism itself may not be provided. As mentioned above, when there is no need to have the motor in common, it is the best way to mount the motor to the shutter unit.
Apart from the case where a costly and specially constructed motor is used, when a motor which has a long rotary shaft and is advantageous in cost is used as usual, the shutter unit cannot be favorably placed in the casing of the digital still camera if the motor is merely mounted to the shutter unit. Specifically, since the shutter unit must be designed so that it can be used in various digital still cameras as far as possible, it is necessary that, in addition to compactness of the shutter unit itself, the shutter unit is constructed so that, for example, the design of appearance of the camera is not restricted as far as possible; an electric part, such as a cell which requires a great volume, is placed without difficulty; and the placement of a mirror mechanism does not offer an obstruction. When these requirements are synthesized, it is required that the front-to-back dimension of the camera is reduced as far as possible.
It is, therefore, a primary object of the present invention to provide a focal-plane shutter for digital still cameras which allows an imaging surface to be exposed through a slit provided by the first blade and the second blade and which is favorably applied to a camera equipped with an electronic view finder and is suitable for compact design.
It is another object of the present invention to provide a focal-plane shutter for digital still cameras in which the shutter blade is actuated by a spring in photography and a motor is actuated against the biasing force of the spring in cocking operation and which offers a compact design even when the motor is mounted to the shutter unit, and can be used in relatively many kinds of cameras.
In order to achieve the above objects, according to one aspect of the present invention, the focal-plane shutter for digital still cameras includes a first blade and a second blade, each having a plurality of arms pivotally mounted on a shutter base plate and at least one blade component pivotally supported thereby; a driving member for the first blade, actuated by the biasing force of a driving spring for the first blade to open an exposure aperture through the first blade when an exposure operation is performed; a driving member for the second blade, actuated by the biasing force of a driving spring for the second blade to close the exposure aperture through the second blade when the exposure operation is performed; a retaining means for the first blade and a retaining means for the second blade, retaining the driving member for the first blade and the driving member for the second blade, respectively, at positions where the exposure operation is started, immediately before the exposure operation is started, and releasing their retaining forces at preset timing when the exposure operation is started; and a cocking member for actuating the driving member for the second blade against the biasing force of the driving spring for the second blade when moved from the initial position to the cocked position thereof, stopped once at a temporary stop position where the exposure aperture is fully opened by the second blade and then moved from this position to a cocked position in photography so that the driving member for the first blade is actuated against the biasing force of the driving spring for the first blade and after the exposure aperture is closed by the first blade, the cocking member is restored to the initial position from the cocked position before the exposure operation is started by each driving member.
In the focal-plane shutter for digital still cameras of the present invention, when the cocking member is a rotary member with a wheel, designed so that its rotation is controlled by a motor, the stop at the temporary stop position and the control of the operation start can be easily made.
In the focal-plane shutter for digital still cameras of the present invention, when the cocking member is restored to the initial position from the cocked position, the amount of movement of the cocking member can be decreased, compared with the case where the cocking member is moved in only one direction, if the cocking member is moved in a reverse direction with respect to the direction in which it is moved from the initial position to the cocked position.
In the focal-plane shutter for digital still cameras of the present invention, when each of the retaining means for the first blade and the retaining means for the second blade is constructed with an electromagnet for attracting an iron piece member provided in each of the driving member for the first blade and the driving member for the second member, the construction of the shutter becomes simple.
Furthermore, in the focal-plane shutter for digital still cameras of the present invention, when at least one sensor is provided in order to detect at least one of a closed state of the exposure aperture where the cocking member is located at the initial position, a fully opened state of the exposure aperture where the cocking member is located at the temporary stop position, and a closed state of the exposure aperture where the cocking member is located at the cocked position, each of the above positions can be checked, and it becomes possible to grasp an abnormal operation of the shutter with accuracy.
In this case, when the at least one sensor is designed to detect the moving position of the cocking member or a transmission member provided between the motor and the cocking member, the mechanism of the shutter becomes simple.
According to another aspect of the present invention, the focal-plane shutter for digital still cameras includes two base plates between which a blade chamber is provided, having object optical path apertures, one for each of the base plates, so that an exposure aperture is restricted by one or both of them; at least one opening and closing means constructed with a plurality of arms pivotally mounted on one of the two base plates within the blade chamber in a region which lies on one of right and left sides of the exposure aperture in an ordinary photographing posture and at least one blade component pivotally supported by the plurality of arms, opening and closing the exposure aperture in a vertical direction in the photographing posture; at least one driving means connected to one of the plurality of arms of the opening and closing means and attached to one of the two base plates outside the blade chamber in the region so that the opening and closing means is actuated by the biasing force of a driving spring in photography; at least one retaining means retaining the driving means at a position where an operation on the driving spring is started so that its retaining force is released in photography; at least one motor mounted to one of the two base plates so that a lengthwise direction of its rotary shaft is nearly parallel to the vertical direction at a position in the region, farther away from the exposure aperture than the position of the driving means; and at least one cocking means actuated by the motor between an initial position and a cocked position so that when it is moved from the initial position to the cocked position, the driving means is actuated against the biasing force of the driving spring, and restored to the initial position, at latest, before the driving means starts to operate in photography.
In the focal-plane shutter for digital still cameras of the present invention, when the retaining means is constructed with an electromagnet and the driving means is provided with an iron piece member attracted to the electromagnet, a direct type shutter which is simple in structure can be obtained.
In the focal-plane shutter for digital still cameras of the present invention, when two opening and closing means, two driving means, and two retaining means are provided and one motor and one cocking means are placed, a shutter for making exposure through a slit provided by the first blade and the second blade is favorably obtained.
In the focal-plane shutter for digital still cameras of the present invention, the driving means may be mounted to one of the two base plates and the motor may be mounted to the other.
In the focal-plane shutter for digital still cameras of the present invention, the driving means and the motor may be mounted to the same one of the two base plates. In this case, when the shutter is designed so that a part of the motor is directed toward a base plate to which the motor is not mounted, of the two base plates, and projects within the limit of up to the surface, on the opposite side of the blade chamber, of the base plate, is this may be advantageous for compactness of the camera.
In the focal-plane shutter for digital still cameras of the present invention, when the shutter is incorporated in the camera, the driving means and the motor are placed to lie in the proximity of or in a space provided by the grip of a camera body. By doing so, the design of the camera will not be spoiled.
These and other objects as well as the features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings.